I have read numerous forums and articles about mp3 cbr and vbr, some swear by cbr others vbr, the debate just goes on and on. I,ve tried cbr 256, vbr 256, cbr 320, cbr 192 cbr etc and I cant hear any difference. My question is why bother with cbr or vbr, why dont people just go with MP3 ABR, would this not be the ideal compromise, or I am missing something, as there does seem to be lack of mp3 abr on offer as downloads from the likes of Napster etc.

Also ABR / CBR is inferior to VBR in terms of pre-echo control. V5 can outdo ABR 170k in impulse handling. When using higher bitrate - 224 ~ 320k CBR / ABR converges so yes below that you could be getting the worst of everything. At high bitrate there might be an advantage: predictable size, max hardware compatibility, theoretical safety from aggressive VBR compression when psymodel is failing.

Yes but CBR is underrated and doesn't fully 'starve' since lame uses a bit reservoir . Its just a little dumb that it encodes digital silence. Also ABR is really VBR without letting psymodel full control over bitrate so if some crazy player doesn't like VBR then its very possible that it doesn't like ABR. ABR might be the worse of everything in such case. I think it might have a niche at high bitrate 230 ~ 300 k or when going lower than 120 k.. likewise CBR 192 ~ 256 k is a good option for high quality / good size + 100% compatibility for every software and device ever made.

There's no getting around that in MP3, but unless you use the -F option, LAME will actually use low-bitrate frames for digital silence, even in CBR mode.

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Also ABR is really VBR without letting psymodel full control over bitrate

The documentation says that ABR is more like CBR in that actual quantization noise is not taken into account; rather, a prediction of the space needed for a frame is made by some other means. So I would look at ABR as more like "CBR with less restrictions on bitrate" rather than "VBR with more". Unless I'm not understanding something.